The invention relates to improvements in method and device for producing a profiled body of at least one band of material which is profiled by a series of successive forming steps by means of pairs of rotating forming tools.
More particularly this invention relates to an improvement of the method described in the U.S. Pat. No. 3,841,134. According to the former method profiled rails and bodies composed thereof are made of at least one metal band by carrying out the following forming steps.
Introducing initial undulations into parts of the band to facilitate subsequent profiling of the band by bending it at bending points between rotating pairs of forming rolls: PA0 Determining a directrix subdividing the metal band into a first area extending from on exterior edge to said directrix, and a second area extending from the other exterior edge to said directrix, said directrix coinciding with a marked longitudinal edge to be formed into the metal band; PA0 Turning at least one of said areas about said directrix so that the exterior edge associated with said area performs a swinging motion while the transverse distance of said associated exterior edge from said directrix is reduced step-by-step throughout the continuous forming process, thereby reducing accrued edge tensile stresses; PA0 Increasing said initial undulations of said parts of said band until the enveloping lines of said parts transverse to the metal band become longer than the enveloping of the longitudinal profile contemplated for said parts thereby leaving surplus width whereby no thinning of the band will occur during subsequent upsetting; and PA0 Transversely upsetting said metal band at said bending points using the surplus width created by increasing said undulations, and bending the metal band with a curvature smaller than the band thickness into sharp-edged profile structures.
The method of the aforesaid patent further comprises exerting a longitudinal tractive force on the metal band by a subsequent pair of rolls as the metal band passes between at least some of the pairs of forming rolls by the roll surfaces of said subsequent pair of rolls being driven at a higher circumferential speed than the corresponding roll surfaces of the preceding pair of rolls. The circumferential speed of said subsequent pair of rolls is higher by at least 0.2 per cent than that of the preceding pair of rolls.
According to the former method a first and second metal band may be formed simultaneously, the second metal band being twisted from its initial position during the continuous forming, profiled, and placed in a predetermined position relative to a profiled rail formed from the first metal band, and indetachably connected to the latter to make a profiled body. Both rails are connected by fold-type connection along their longitudinal borders, the longitudinal borders being forced together and are one longitudinal edge of one rail being bent around the associated longitudinal border of the other rail, the two longitudinal borders thereby becoming indetachably interconnected.
One difficulty arising in the step-by-step forming by means of rotating forming tools resides in the necessary large number of consecutive forming steps in consequence that only a small forming of the band per forming step is admissable due to the tension stresses in the exterior edges which otherwise would cause a undesired formation of tears or permanent elongations in the edges. Roll forming machines adapted for producing complicate profiled bodies normally comprise 20 - 30 subsequent forming stations.
In the aforesaid patent it has already been suggested to reduce the tensile stresses in one edge of the band by determing a directrix on the band and turning the band area between said edge and the directrix about the directrix.
It has been found that this ideal of turning a band area about a directrix may further be developed. Resulting is a new technical prescription for the forming process by which application a considerable reduction of the tensile stresses in one of the edges of a band during its profiling is obtained.
According to the present invention the first forming steps are introducing initial undulations into parts of said band to facilitate profiling of the band during subsequent forming steps. At least one directrix is determined on the band for some of the forming steps, said directrix coinciding with a prominent longitudinal edge of the body and subdividing the band into a first and second band area, the first area extending from one exterior edge of the band to said directrix, the second area extending from the other exterior edge of the band to said directrix. The improvement of the present method comprises: carrying out at least some forming steps by swinging said first area about the directrix in a first direction and simultaneously swinging said second area about the directrix in opposite direction to said first direction towards said first area in order to reduce tensile stresses in one of said exterior edges at the cost of increasement of tensile stresses in the other exterior edge.
Hence one object of the present invention is to provide an improved method for forming profiled bodies which allows a reduction of the number of forming steps.
A further object is to provide improved subsequent forming stations for a forming machine which may replace a greater number of forming stations known in the art.
These objects and the features of the present invention will become more clearly apparent from the subjoined specification and claims when considered in connection with the drawing illustrating some embodiments and when considered in connection with the appended claims.